Vehicle door-opening cam track arrangement

ABSTRACT

A ground-mounted elevatable cam track arrangement for operating railroad car mounted hopper discharge door operating linkage, which arrangement includes a movable door-operating linkage camsupporting structure, and fixed ground-mounted cam support structure having guide means guiding the upward and downward travel of the movable cam support structure and having hydraulic means raising or lowering the movable cam support structure from the elevated in-use position at the railroad trestle to the lowered out-of-use position at the railroad trestle, and adjusting means for limiting the maximum elevation of the movable cam structure.

United States Patent Inventor Roy W. Miller Highland, Ind.

Appl. No. 873,791

Filed Nov. 4, 1969 Patented Jan. 11, 1972 Assignee Pullman IncorporatedChicago, Ill.

VEHICLE DOOR-OPENING CAM TRACK ARRANGEMENT 12 Claims, 9 Drawing Figs.

U.S. Cl 214/63, 105/241 C Int. Cl B61d 7/30 Field of Search... 214/58,63;

iilrtn l .iiliii [56] References Cited UNITED STATES PATENTS 3,080,0753/1963 Giesking 2l4/63 3,471,044 10/1969 Aguino et al. 2 l 4/63 PrimaryExaminer- Robert G. Sheridan AttorneysHilmond O. Vogel and Wayne MorrisRussell ABSTRACT: A ground-mounted elevatable cam track arrangement foroperating railroad car mounted hopper discharge door operating linkage,which arrangement includes a movable door-operating linkagecam-supporting structure, and fixed ground-mounted cam support structurehaving guide means guiding the upward and downward travel of the movablecam support structure and having hydraulic means raising or lowering themovable cam support structure from the elevated in-use position at therailroad trestle to the lowered out-of-use position at the railroadtrestle, and adjusting means for limiting the maximum elevation of themovable cam structure.

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HHIIIII (40 u "T hi INVE N TOR 7| ROY W MILLER MHIHH PATENTED JAN] 1I972 SHEET 3 BF 5 INVENTOF? ROY w MILLER Nw zwmo oh 1 wm o o 8 mm ATWPATENTED JAN! 1 1972 SHEET 4 0F 5 INVENTDR ROY W MILLER fiM x PATENTEDJAN] 1 I972 SHEET 5 [1F 5 (NVENTOR ROY W. MILL ER TT'Y VEHICLEDOOR-OPENING CAM TRACK ARRANGEMENT SUMMARY This invention relates toground-mounted cam-supporting structure for engaging the door-operatinglinkage of the discharge doors of a hopper railroad car for opening andclosing of the hopper doors.

It is therefore a general object of this invention to provide novel camsupport structure for engagement with the hopper doors of a railroad carat certain times and not at other times.

A further objective of this invention is to provide for an elevatablecam support structure for the hopper car which may be raised to anin-use position and lowered to an out-ofuse position at the railroadtrestle.

Another objective of this invention is to provide hydraulic means forraising and lowering the door-operating linkage engaging cam structureattendant to opening and closing the hopper doors of the car, andfurther to raise one of two portions of said cam-supporting structureand then the second portion to sequentially clear the locomotive and yethaving opening of the doors of the first of series of cars connected tothe locomotive.

A further objective of this invention is to provide for movableadjusting means for limiting the maximum elevation of the door-actuatingcams attendant to opening and closing the hopper doors of the car.

These and other objectives and advantages will become apparent fromreference to the attached drawings, the following description, and theappended claims.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view of therailroad car illustrating the cam support arrangement and the hopper cardoor operating linkage;

FIG. 2 is a perspective view, partially in section, showing thecam-supporting structure that carries the door-operating ground-mountedcam means;

FIG. 3 is a top plan view similar to FIG. 2;

FIG. 4 is a side elevational view taken along line 44 of FIG. 3;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 3;

FIG. 6 is a top sectional view showing the door-operating linkage withthe doors in the closed position;

FIG. 7 is a cross-sectional elevational view showing the operation ofthe door-operating linkage with the doors in the open position;

FIG. 8 is a schematic view illustrating the operation and positioning ofthe drive cam engaging lever of the dooroperating mechanism as the doorsmove to the open position; and

FIG. 9 is a schematic view of the door operating cam engaging lever asthe doors move to the closing position.

DETAILED DESCRIPTION With reference now to the drawings, there is showna railroad hopper car 2, as seen in FIGS. 1, 6, and 7, having sides 4,end 6 and side sills 7, a center sill 8, and door-operating supportingstructure 10 carrying door-operating mechanism 16 for operating thedoors 14 of the car hoppers 12. The car 2 is movably supported on thetrucks l8 and rides over the car wheel-engaging rails 20. Thedoor-operating mechanism 16 is of the type disclosed in the copendingU.S. patent application Ser. No. 598,440 filed on Dec. I, 1966 byWilliam R. Shaver, now U.S. Pat. No. 3,459,317 issued Aug. 5, I969,incorporated by reference. The door-operating mechanism 16 includeslinks 19 and door-operating anns 22 connecting with the doors l4 andwith the crank structure 24, as seen in FIGS. 6 and 7, having an uppercrank 21, an intermediate crank 23 and a lower crank 25, the crankstructure 24 being engaged with the overcenter crank stop means 27 whenthe vehicle doors and the door-operating mechanism are in the closeddoor position. Each crank structure 24 is connected by transfer links26, one crank structure 24 fixedly supporting a drive lever 28 havingcam follower rollers 29 and 29a and connected by arm 28a to lower crank25.

The door-operating mechanism 16 is constructed and arranged to engagethe cam track means 30 as the railroad car passes over the cam trackmeans 30 mounted on the trestle side members 45, 46 at a certain dumpingsite on the railroad rails or tracks 47. The cam track means 30 includesthe offvehicle ground-mounted door-actuating cam means 31 which issupported by the ground-supporting structure 32. The ground-mountedcam-supporting structure 32 comprises the fixed ground support means orunit 33 and the movable cam support structure 330 which is best seen inFIGS. 25. The drive lever 28 has one of its cam follower rollers 29 or290, depending in which direction the car is moving, engage the cammeans 31 which includes an entrant opening cam and closing cam gatestructure 34, a fixed cam element 35, a door-opening idle cam member 36,a second fixed cam structure 38, an opening gate and entrant closing camstructure 39, a fixed closing gate element 41, and a pivotal closinggate member 42. The cam structure 34 includes an entrant cam surface 34aand the fixed cam element includes an opening cam surface 350. The idlecam member 36 has an idle cam surface 36a and the cam element 41 issupported by the cam support structure 37. The cam element 38 has anopening cam surface 38a and the cam structure 39 has an opening cam gatesurface 39a. The gate structure 39 has a pivot means 40a and engages thefixed opening cam gate stop 40. The closing cam structure 39 is providedwith a closing cam surface 39b and the cam element 38 is provided withthe closing cam surface 381;. The cam element 4] is provided with aclosing cam surface 41a and the vertical closing cam member 42 isprovided with a closing cam surface 42a and closing cam surface 421;. Abiasing spring unit 43 connects the biasing arm 43a which pivots pivotalcam member 42 about its pivotal arm 420. The closing cam gate structureis provided with a closing gate 34b and has a closing cam gate stop 44and a pivot means 44a. The construction and arrangement of these camelements is particularly seen in FIGS. 3 and 5. The detailedconstruction and operation of the opening and closing cam elements 34,35, 38, 39, 41, and 42 is disclosed in the copending patent applicationSer. No. 838,572, filed July 2, 1969 to James J. Schuller, which ishereby incorporated by reference. It suffices to say here that, as seenin in FIGS. 8 and 9, as the drive lever 28 passes from right to left thedrive lever is rotated in a counterclockwise direction by engagementwith the various aforesaid cam elements to completely open the hopperdoors of the vehicle and when the drive lever passes by these variouscam elements from left to right in the closing direction the drive leveris rotated 180 in a clockwise direction to fully close the hopper doors.Auxiliary lock guide rail means 32a are provided on the movable camsupport means 33a for engaging with the auxiliary lock means on therailroad car which prevents accidental movement of the drive lever 28 sothat the doors cannot accidentally open, the auxiliary lock means beingshown in particular in the copending patent application Ser. No. 618,152filed Feb. 23, 1967 to Herman A. Aquino, now U.S. Pat. No. 3,515,076issued June 2, 1970, and hereby incorporated by reference.

With particular reference to FIGS. 2-5, the cam-supporting structure 32,carrying the door-operating cam means 31, has

its fixed ground support structure 33 comprised of a pair of I laterallyspaced end crossmembers 50 attached to the longitudinally extendingtrestle side members 45 and 46. Each end crossmember 50 is composed ofan end l-beam 48 and an end U-shaped or channel beam 49. The beams 50are attached by bolts 52 to the reinforcing sideplates 51 attached tothe side trestle beam members 45, 46 over which extend the rails 47.

The fixed cam-supporting structure 33 is provided with a plurality offixed guide posts or lower guide tubes 55 which form part of theadjustable guide means 60. Each guide post 55 consists of an elongatedvertical tube, there being four such tubes for carrying each of twomovable cam-supporting structures 64, 65 to be later described. Asviewed in FIG. 4 the extreme left posts 55 and the extreme right posts55 are each supported by an end tube tie plate assembly or box structure54 whereas the center tubes 55 are supported by a center tube tie plateassembly or box 53. These assemblies 53 and 54 are main transversesupport structures for the lower fixed cam support structure and tieinto the longitudinally extending side members 56d of the fixedground-mounted cam support 33.

The tube tie plate assembly or box 53 includes the top and bottom posttie plates 53a and 53b which are provided with post-receiving aperturesor holes 53d and through which the posts 55 extend and are attachedthereto. The plates 53a and 53b connect with outer cross-channel members530 of the box 53. Similarly each of the end tie plate assemblies orboxes 54 has top and bottom plates 54a, 54b and end channel members 54c,the plates 54a and 54b being also suitably apertured for receiving andholding a fixed upright end tube 55.

The lower or fixed cam support assembly 33 is also provided with rightand left hydraulic unit supporting cradles 56 and 57. The rightsupporting cradle 56 is provided with upright end plate 56a attaching tothe channels 530 and 54c and the left support cradle 57 is provided withupright end plates 57a connecting with the beams 53c and 54c. The cradle56 is provided with longitudinally extending member 56b and gussets 56c,and the cradle 57 is provided with longitudinally extending member 57band gussets 570. The cradle 56 carries by means of pivot means 58c thehydraulic means of the unit 58 and the cradle 57 pivotally carries bymeans of pivot 590 the hydraulic means 59. The hydraulic unit 58includes cylinder 58a, piston rod 58b, and a rod pivot means 58dconnecting with the right upper movable cam support structure 65 of themovable cam support means 33a. The hydraulic jack means 59 has acylinder 59a and a pivot rod 59b which connects with the rod pivot means59d to which is attached the left upper movable cam support structure 64of the movable cam support means 33a. The adjustable guide means 60 inaddition to including the lower fixed guide tubes 55 also includes theupper movable tubes 61 each being reciprocally extendable over itsrespective tube 55 and connected therewith by adjusting means 62 whichincludes a bolt 62a and a nut 62b, the bolt 62a extending throughaperture cap 55a of the tube 55 and through aperture cap 61a of themovable tube 61. The adjusting means is best seen in FIG. 4 which showsthe maximum extension of the upper tube 61 with respect to the lowertube 55 permissible, such extension being reducible by moving bolt 620on the nut 62b. Gussets 63 tie the upper tubes 61 to units 64 and 65.

' The upper movable cam-carrying unit 64 is provided with longitudinalside members 66 and channel-shaped crossmembers 67, the bottom of theside members 64 being provided with angle iron members 66a. The uppermovable cam support structure 65 is provided with longitudinal sidemembers 68 each having an angle iron bottom member 68a and withchannel-shaped crossmembers 69. The cam support structure is providedwith diagonal cam support 70 and horizontal longitudinal bottom camsupport member 71 to which attaches hydraulic unit 59. The upper movablecam support structure 65 has diagonal cam support members 72 andhorizontal longitudinal extending movable cam support member 73 to whichis attached the hydraulic means 58. The cam support structure 65 isfurther provided with horizontal transverse cam support member 74. Thecam support structure 64 carries cam members 38 and 39 and the movablecam support structure 65 carries cam members 34, 35, 36, 37, 41, and 42as best seen in FIG. 3.

By such an arrangement it is seen that the elevatable cam supportstructures 64 and 65 may be raised and lowered for raising and loweringtheir respective cam members attendant to the opening and closing of thehopper doors, the maximum extension of a movable cam support structureabove its fixed base support structure being limited by suitableadjusting means. A series of coupled cars are pulled by the locomotiveand it at times may be desirable to first elevate the cam supportstructure 65 as it clears the rear end of the locomotive and then tosubsequently raise the second movable cam support structure 64 as itclears the locomotive in order to insure that the lead hopper car may beopened and, of course, later closed by both of the cam supportstructures 65 and 64, since the bottom of the locomotive is usuallycloser to the ground than the bottom of the hopper car and wouldinterfere with the cam units if they were in the raised condition as thelocomotive passed thereover. ln reversing the locomotive after thehopper doors of all the cars have been opened for dumping it will beappreciated that the movable cam support structure 64 would first belowered and then the structure 65 to insure closing of the hopper doorsof the first car connected to the locomotive and yet to have the camsupport structures 64 and 65 lowered in sequence in order to clear thebottom of the locomotive.

The foregoing description and drawings are given merely to explain andillustrate the invention and the invention is not to be limited thereto,since those skilled in the art who have the disclosure before them willable to make modifications and variations therein without departing fromthe scope of the invention.

What is claimed is: l. A ground-mounted cam track arrangement forengaging the hopper door operating structure of a hopper railroad carpassing over the track arrangement comprising:

a fixed cam track support structure adapted for securement at thetrestle side structure supporting the railroad tracks,

said fixed cam track support structure comprising a pair of laterallyspaced apart longitudinally extending fixed side members,

a pair of longitudinally spaced-apart end crossmembers adapted forsecurement with the trestle side structures and connecting said fixedside members,

a pair of longitudinally spaced cradle members each being adapted tosupport a hydraulic means, and connecting with a respective endcrossmember,

intermediate transverse support means connecting with the fixed sidemembers and tying the cradle members together,

a movable cam track support structure disposed above said fixed camtrack support structure and including a pair of longitudinallyspaced-apart independently vertically movable cam track support units,

hopper door-operating cam means carried on each movable cam tracksupport unit operative to open and close the hopper doors of therailroad car,

first elevating hydraulic means connecting one cradle member with onemovable cam track support unit and a second elevating hydraulic meansconnecting the other cradle member with the other movable cam tracksupport unit, each of said movable cam support units havinginterconnected spaced apart side members and spaced-apart endcrossmembers and having cam-carrying beam means,

vertical guide means operatively connecting each movable cam unit witheach of the fixed structure end cross struc tures and with theintermediate transverse means,

said vertical guide means comprising a plurality of fixed vertical postsconnecting with the end crossmembers and the intermediate transversemeans, said vertical guide means including a plurality of movable guideposts on each of the movable units and connecting with the respectivefixed posts and reciprocal therewith for vertically guiding of the saidmovable units when each of the hydraulic means selectively operates toraise and lower the movable units with respect to the fixed cam supportstructure, and

adjusting means limiting the maximum travel of each of the movable unitscomprising rod means connecting said fixed post with each movable postand adjustably limiting the maximum elevation of the movable post abovethe fixed post.

2. A ground-mounted cam track arrangement for engaging the hopperdoor-operating structure of a hopper railroad car passing over the trackarrangement comprising:

a fixed cam track support structure,

a movable cam track support structure disposed above said fixed camtrack support structure,

hopper door operating cam means carried on the movable cam track supportstructure,

elevating means connecting with said fixed cam track support structureand with said movable cam track support structure for verticallyreciprocating the movable cam track support structure with respect tosaid fixed cam track support structure,

vertically extendable guide means on each of said cam track supportstructures for vertically guiding one structure with respect to theother, and

adjusting means on said vertical guide means adjustably limiting themaximum travel of the movable cam track support structure with respectto said fixed cam track support structure,

said movable cam track support structure including a pair of separateindependently movable units and said fixed cam track support structureincluding a pair of separate fixed units, said elevating means includingmeans moving one movable unit independently of the other.

3. A ground-mounted cam track arrangement for engaging the hopper dooroperating structure of a hopper railroad car passing over the trackarrangement comprising:

a fixed cam track support structure,

a movable cam track support structure disposed above said fixed camtrack support structure,

elevating means connecting with said fixed cam track support structureand with said movable cam track support structure for verticallyreciprocating the movable cam track support structure with respect tosaid fixed cam track support structure,

vertically extendable guide means on each side of said cam track supportstructures for vertically guiding one structure with respect to theother,

said movable cam track support structure including a pair oflongitudinally spaced-apart independently vertically movable cam tracksupport units reciprocally carried on said fixed cam track supportstructure,

said elevating means including means raising one movable unitindependent of the other, and

hopper door-operating cam means carried on each movable cam support unitoperative to open and close the hopper doors of the railroad car.

4. The invention according to claim 3, and

said fixed cam track support structure comprising a pair of laterallyspaced apart longitudinally extending side beams, and

a pair of longitudinally spaced-apart end crossbeams adapted forsecurement with railroad trestle side units and connecting with saidfixed side beams, and

elevating means support means adapted to support said elevating meansand connecting with the end crossbeams.

5. The invention according to claim 3, and

said elevating means comprising hydraulic jack means interconnecting thefixed and movable cam support structures.

6. The invention according to claim 3, and

said vertically extendable guide means comprising a plurality of fixedvertical posts on the fixed cam track support structure and acomplemental number of movable guide posts fixed on said movable camtrack support structure and reciprocally interconnectedly disposed withrespect to said fixed posts for maintaining vertical alignment of onecam support structure with respect to the other.

7. The invention according to claim 3, and

adjusting means interconnecting the cam track support structureslimiting the maximum travel of the movable cam track support structurewith respect to the underposed fixed cam track support structure.

8. The invention according to claim 7, and

said adjusting means comprising rod means interconnecting the respectivecam support structures and bein lengthwise ad ustable to vary themaximum travel of one cam track support structure with respect to theother.

9. The invention according to claim 3, and

said fixed cam track support structure comprising a pair of longitudinalbeams interconnected with end crossbeams to define a general boxlikestructure, transverse structural elements disposed within said boxstructure and supporting said elevating means, and

cam means carried on the movable cam track support structure.

10. The invention according to claim 3, and

said movable cam track support unit comprising a pair of longitudinallyextending side beams and end crossbeams to define a movable boxstructure.

11. The invention according to claim 3, and said fixed cam track supportstructure comprising apair of longitudinal beams interconnected with endcrossbeams to define a general boxlike structure, transverse structuralelements disposed within said box structure and supporting saidelevating means,

each movable cam track support unit comprising a pair of longitudinallyextending side beams and end crossbeams to define a movable boxstructure, and

said elevating means including a pair of elevating units and eachmovable box structure connecting with a respective elevating unit.

12. The invention according to claim 11, and

said guide means including a plurality of fixed vertical posts on thefixed box structure at the ends and middle thereof between each of theelevating units, and said guide means having a plurality of postsconnecting with each of the movable box structures and with the fixedposts whereas one movable box structure may be elevated independently ofthe other movable box structure.

1. A ground-mounted cam track arrangement for engaging the hopper dooroperating structure of a hopper railroad car passing over the trackarrangement comprising: a fixed cam track support structure adapted forsecurement at the trestle side structure supporting the railroad tracks,said fixed cam track support structure comprising a pair of laterallyspaced apart longitudinally extending fixed side members, a pair oflongitudinally spaced-apart end crossmembers adapted for securement withthe trestle side structures and connecting said fixed side members, apair of longitudinally spaced cradle members each being adapted tosupport a hydraulic means, and connecting with a respective endcrossmember, intermediate transverse support means connecting with thefixed side members and tying the cradle members together, a movable camtrack support structure disposed above said fixed cam track supportstructure and including a paIr of longitudinally spaced-apartindependently vertically movable cam track support units, hopperdoor-operating cam means carried on each movable cam track support unitoperative to open and close the hopper doors of the railroad car, firstelevating hydraulic means connecting one cradle member with one movablecam track support unit and a second elevating hydraulic means connectingthe other cradle member with the other movable cam track support unit,each of said movable cam support units having interconnected spacedapart side members and spaced-apart end crossmembers and havingcam-carrying beam means, vertical guide means operatively connectingeach movable cam unit with each of the fixed structure end crossstructures and with the intermediate transverse means, said verticalguide means comprising a plurality of fixed vertical posts connectingwith the end crossmembers and the intermediate transverse means, saidvertical guide means including a plurality of movable guide posts oneach of the movable units and connecting with the respective fixed postsand reciprocal therewith for vertically guiding of the said movableunits when each of the hydraulic means selectively operates to raise andlower the movable units with respect to the fixed cam support structure,and adjusting means limiting the maximum travel of each of the movableunits comprising rod means connecting said fixed post with each movablepost and adjustably limiting the maximum elevation of the movable postabove the fixed post.
 2. A ground-mounted cam track arrangement forengaging the hopper door-operating structure of a hopper railroad carpassing over the track arrangement comprising: a fixed cam track supportstructure, a movable cam track support structure disposed above saidfixed cam track support structure, hopper door operating cam meanscarried on the movable cam track support structure, elevating meansconnecting with said fixed cam track support structure and with saidmovable cam track support structure for vertically reciprocating themovable cam track support structure with respect to said fixed cam tracksupport structure, vertically extendable guide means on each of said camtrack support structures for vertically guiding one structure withrespect to the other, and adjusting means on said vertical guide meansadjustably limiting the maximum travel of the movable cam track supportstructure with respect to said fixed cam track support structure, saidmovable cam track support structure including a pair of separateindependently movable units and said fixed cam track support structureincluding a pair of separate fixed units, said elevating means includingmeans moving one movable unit independently of the other.
 3. Aground-mounted cam track arrangement for engaging the hopper dooroperating structure of a hopper railroad car passing over the trackarrangement comprising: a fixed cam track support structure, a movablecam track support structure disposed above said fixed cam track supportstructure, elevating means connecting with said fixed cam track supportstructure and with said movable cam track support structure forvertically reciprocating the movable cam track support structure withrespect to said fixed cam track support structure, vertically extendableguide means on each side of said cam track support structures forvertically guiding one structure with respect to the other, said movablecam track support structure including a pair of longitudinallyspaced-apart independently vertically movable cam track support unitsreciprocally carried on said fixed cam track support structure, saidelevating means including means raising one movable unit independent ofthe other, and hopper door-operating cam means carried on each movablecam support unit operative to open and close the hopper doors of therailroad car.
 4. The invention according to claim 3, and said fixed camtrack support structure comprising a pair of laterally spaced apartlongitudinally extending side beams, and a pair of longitudinallyspaced-apart end crossbeams adapted for securement with railroad trestleside units and connecting with said fixed side beams, and elevatingmeans support means adapted to support said elevating means andconnecting with the end crossbeams.
 5. The invention according to claim3, and said elevating means comprising hydraulic jack meansinterconnecting the fixed and movable cam support structures.
 6. Theinvention according to claim 3, and said vertically extendable guidemeans comprising a plurality of fixed vertical posts on the fixed camtrack support structure and a complemental number of movable guide postsfixed on said movable cam track support structure and reciprocallyinterconnectedly disposed with respect to said fixed posts formaintaining vertical alignment of one cam support structure with respectto the other.
 7. The invention according to claim 3, and adjusting meansinterconnecting the cam track support structures limiting the maximumtravel of the movable cam track support structure with respect to theunderposed fixed cam track support structure.
 8. The invention accordingto claim 7, and said adjusting means comprising rod meansinterconnecting the respective cam support structures and beinglengthwise adjustable to vary the maximum travel of one cam tracksupport structure with respect to the other.
 9. The invention accordingto claim 3, and said fixed cam track support structure comprising a pairof longitudinal beams interconnected with end crossbeams to define ageneral boxlike structure, transverse structural elements disposedwithin said box structure and supporting said elevating means, and cammeans carried on the movable cam track support structure.
 10. Theinvention according to claim 3, and said movable cam track support unitcomprising a pair of longitudinally extending side beams and endcrossbeams to define a movable box structure.
 11. The inventionaccording to claim 3, and said fixed cam track support structurecomprising a pair of longitudinal beams interconnected with endcrossbeams to define a general boxlike structure, transverse structuralelements disposed within said box structure and supporting saidelevating means, each movable cam track support unit comprising a pairof longitudinally extending side beams and end crossbeams to define amovable box structure, and said elevating means including a pair ofelevating units and each movable box structure connecting with arespective elevating unit.
 12. The invention according to claim 11, andsaid guide means including a plurality of fixed vertical posts on thefixed box structure at the ends and middle thereof between each of theelevating units, and said guide means having a plurality of postsconnecting with each of the movable box structures and with the fixedposts whereas one movable box structure may be elevated independently ofthe other movable box structure.